1. Yes, Monday is always the first day of the week on UK calendars.
2. There are no fixed conventions, but some calendars print the weekday dates in black, Saturdays in blue, and Sundays and Bank Holidays in red. Some have both weekend days in red, while others don't differentiate at all.
3. Bank Holidays are always shown, as these are always fixed a few years in advance. And yes, we expect to have them marked on our calendars.